My last Instructable was about making "A Small Bedside Coffee Table in Concrete" using easily available household items, which you can view at this link: https://www.instructables.com/id/A-Small-Bedside-Coffee-Table-in-Concrete/
This Instructable will provide you step-by-step guide on how to replicate an artifact in concrete using a mold made of silicone rubber.
I came across this piece of art of 'a mother bird feeding its chicks on a tree branch' and wanted to make a copy of that. So I borrowed the piece, made a mold out of silicone rubber and using that mold cast it in concrete.
Look at the original and the replications in these pictures.. Though there are some imperfections in the replication, they can be corrected using a paste made of white cement and cement pigment. Also. for drawing the eyes and all, I will get some friends' help as I am not good at that.
Step 1: How to Make the Silicone Mold...
To replicate this art piece, one of the most suitable mold making material which can bring out the intricate details is Silicone Rubber. I have used Silicone mold making material VITSPEC VSGI-1220. This material comes in two parts, the Base and the Activator. With the 5 kilogram pack of the Base, a 250 grams Activator is included. That means, for every 1000 grams of base, you need to add 50 grams of Activator. After activation, it will take a minimum of 24 hours to fully cure.
- Select a suitable container to hold the piece to be replicated and the silicone mix.
- Roughly calculate the amount of silicone mix needed for the job. I have calculated that I need about 1500 grams of Silicone mix.
- Take a container and weigh about 1500 grams of base.
- Add 75 grams activator to the base and mix well. it is recommended to pour the mix back in another container and mix again uniformly.
- Spray the art piece and the container with silicone spray, which will act as mold release.
- Pour the silicone mix over the container from a height of about 12 inches, starting from the exposed lower end and follow it up so that the mix naturally flows up and covers all the curves, nooks and corners without trapping any air bubbles.
- After completely filling up the container, leave it undisturbed for about 24 hours.
- After 24 hours, lightly touch the top surface of the silicone mix. If it sticks to your fingers, give it more time to cure. As the quantity of mix is more, it took about 48 hours in my case.
- When the silicone mix is not sticky to touch, you can take out the mold out of the container and release the art piece.
Now your Silicone mold is ready. You can replicate as many pieces of the original as you like, using this silicone mold. You can use it for concrete, wax cast and casting with Plaster of Paris.
Let us see how we can cast the art piece in concrete.
Step 2: Making a Dry Mix of Concrete
Making the dry mix for the concrete work:
- Sieve the required quantity of sand with a fine sieve to remove the coarser particles.
- Measure one part of white cement and two parts of sieved sand.
- Add a table spoon of cement based color pigment to the dry mix. I have used black color pigment here.
- Mix well using a ladle to form a uniform dry mix.
Now the dry mix required for the concrete is ready.
Step 3: Concreting the Mold
Concreting the mold:
- Add little amount of water at a time to the dry mix and mix thoroughly.
- The concrete should contain only enough water for proper filling of the mold and not more than required.
- Keep the mold on a piece of thermocol or any other suitable material.
- Transfer the mixed concrete in layers and compact with the ladle, so that all the nooks and corners are properly filled.
- Shake the concrete holding the bottom piece. This will help in releasing any air bubbles trapped inside.
- After some time, say about 10 to 15 minutes, you will find a layer of water forming on top.
- Using old news paper, sponge out the excess water on top.
- Keep the concrete undisturbed for another 24 hours
Step 4: Curing and Removing the Concrete Cast From the Silicone Mold
Curing and Removing the Concrete Cast from the Silicone Mold:
- After 24 hours of casting, place the mold upside down in cold water. This is to prevent any deformation to the top portion of the cast.
- The mold with the concrete are to be cured for three days in cold water.
- After three days, remove the mold from water and carefully remove the cast.
- You can place the demolded piece in water for another one week for more curing.
Now your replicate in concrete is ready...
Step 5: Bottom Line
The silicone mold we made can be used repeatedly for replicating the original piece. You can use wax, plaster of Paris, concrete and any other suitable material for casting. You can also color your work with cement based colors and make it more attractive.
Please enjoy the pictures of the same piece molded in wax and Plaster of Paris here...